1. Field of the Invention
The present invention relates to a brushless DC-motor driving controller for driving and controlling a brushless DC-motor. Particularly, the present invention relates to a brushless DC-motor driving controller for suitably minimizing torque fluctuations in a brushless DC-motor.
2. Description of the Related Art
For conventional brushless DC-motors driven with rectangular waves, for example, a small number of Hall elements, as in the cases of three Hall elements for three phases and five Hall elements for five phases, is used to detect rotor positions to generate position-detecting signals. The generated position-detecting signals are used to detect the relative positional relation between the rotor and armature coils, and commutation positions are determined according to the positional relation.
According to requirements for cost reduction, miniaturization, and high output power, however, the torque constant and ampere-turns increase in conventional brushless DC-motors. Proportionally to the increase in ampere-turns, the armature-current magnetomotive force also increases, thereby increasing torque-form skew for each phase.
In the conventional brushless DC-motors, in which a small number of Hall elements is used to determine commutation positions and to perform rectangular-wave driving, phase-current commutation positions are fixed. In this case, addition of skewed torques in the individual phases, as shown in FIG. 1B, causes torque connection to be discontinuous, thereby causing torque fluctuations, as shown in FIG. 1A. Torque fluctuations cause noise during operation of the brushless DC-motor.
With an electrical power steering device of vehicles which use the conventional brushless DC-motor causing torque fluctuations as its power source, when the steering wheel is slowly rotated, torque fluctuations effect steering sensation; and when the steering wheel is rotated quickly, the fluctuations cause noise.
The present invention has been developed under the above circumstances. A first object of the present invention is to provide a brushless DC-motor driving controller that significantly reduces torque fluctuations in brushless DC-motors. A second object is to provide a brushless DC-motor driving controller that can be used to improve steering sensation and to reduce noise occurrence in electrical power steering devices.
To achieve the described objects, the present invention provides a brushless DC-motor driving controller that uses a position detector, generates a rotation-angle signal representing rotor-rotation angle or a part thereof in high resolution, uses the rotor-rotation signal, and performs rectangular-wave driving. The rotor-rotation signal is used to compensate for an electrical angle corresponding to commutation-position skew in rectangular-wave driving which is caused by armature reaction in a brushless DC-motor.
In this case,,the electrical angle, which correspond to the commutation-position skew in rectangular-wave driving, which is caused by armature reaction in the brushless DC-motor, may be determined by using functions of values representing four operating conditions of normal-rotation driving, inverse-rotation driving, normal-rotation regenerative braking and inverse-rotation regenerative braking, and armature-reaction effects of the brushless DC-motor.
Also, the above-described brushless DC-motor driving controller, which compensates for the electrical angle corresponding to the commutation-position skew in rectangular-wave driving, which is caused by armature reaction in the brushless DC-motor, may be used to drive and control a brushless DC-motor in an electrical power steering device that uses rotation torque of the brushless DC-motor to support forces required for vehicle-wheel steering.
In this case also, the electrical angle corresponding to commutation-position skew in rectangular-wave driving which is caused by armature reaction in the brushless DC-motor may be determined by using functions of values representing four operating conditions of normal-rotation driving, inverse-rotation driving, normal-rotation regenerative braking and inverse-rotation regenerative braking, and armature-reaction effects of the brushless DC-motor.
According to the above, the objects of the present invention, described above, can be achieved, specifically, in the following manner.
The first object of the present invention can be achieved by the brushless DC-motor driving controller that uses a rotation-angle signal so as to compensate for an electrical angle corresponding, to commutation-position skew in rectangular-wave driving, which is caused by an armature reaction in the brushless DC-motor. This allows torque fluctuations in brushless DC-motors to be significantly reduced. The second object of the present invention can be achieved by the brushless DC-motor driving controller that uses the rotation-angle signal to drive and control a brushless DC-motor in an electrical power steering device that uses rotation torque of the brushless DC-motor to support forces required for vehicle-wheel steering. This improves steering sensation in the electrical power steering device, and in addition, minimizes noise occurrence.
Also, the first and second objects of the present invention can be achieved even more effectively because the electrical angle, which correspond to commutation-position skew in rectangular-wave driving which is caused by an armature reaction in the brushless DC-motor, is determined by using functions of values representing four operating conditions of normal-rotation driving, inverse-rotation driving, normal-rotation regenerative braking and inverse-rotation regenerative braking, and armature-reaction effects of the brushless DC-motor.
Furthermore, according to the brushless DC-motor driving controller of the present invention, rotation-angle signals that represent close rotor-rotation angles are used to perform rectangular-wave driving. This allows phase-current commutation positions to be closely controlled.